1. Field of the Invention
The present invention relates to a suspension of a steering vehicle wheel in a vehicle such as an automobile, and more particularly, to an improvement of a double wishbone type suspension of a steering vehicle wheel in the requirement of a mounting space therefor and further in a camber variation performance according to bounding and rebounding of the steering vehicle wheel.
2. Description of the Prior Art
A steering vehicle wheel in a vehicle such as an automobile is generally supported by a knuckle which in turn is supported by a suspension link mechanism via a king pin to be able to turn about the axis of the king pin. The suspension link mechanism is known in various constructions one of which is known as the double wishbone type link mechanism which generally comprises upper and lower arms extending substantially in parallel with one another and transversely in the vehicle from their inner ends pivotably connected with a body of the vehicle to their outer ends pivotably connected with an upper portion and a lower portion of the knuckle, respectively, so as to form a parallelogrammic link mechanism composed of the upper and lower arms, the vehicle body and the knuckle, thus the knuckle being shiftable up and down relative to the vehicle body in the bounding and rebounding of the vehicle wheel, generally under a downward biasing force applied by a suspension spring mounted between the parallelogrammic link mechanism and the vehicle body.
A typical construction of such a double wishbone type suspension is shown in FIG. 1 in a diagrammatical illustration as a front or a rear view looked in the longitudinal direction of the vehicle. In this figure, 100 is a steering vehicle wheel bearing a tire 102 and supported to be rotatable about a central axis thereof by a knuckle 104 which in turn is supported by a body 106 of a vehicle via an upper arm 108 and a lower arm 110. The upper arm 108 extends substantially transversely in the vehicle from its inner end pivotably connected with the vehicle body 106 via a pivot joint 112 to its outer end pivotably connected with an upper portion of the knuckle 104 via a pivot joint 114. The lower arm 110 also extends substantially transversely in the vehicle from its inner end pivotably connected with the vehicle body 106 via a pivot joint 116 to its outer end pivotably connected with a lower portion of the knuckle 104 via a pivot joint 118. As is well known in the art, the upper and lower arms 108 and 110 are generally constructed as an A-type or an H-type link or in a similar construction having a substantial width so that the pivot joints 112 and 116 for the inner ends of these transverse arms are each provided as a pair of joints spaced in the longitudinal direction of the vehicle, thereby providing a rigidity to said parallelogrammic link mechanism against a turning relative to the vehicle body in the longitudinal directions of the vehicle, while said parallelogrammic link mechanism is readily deformable in a vertical phantom plane so that the knuckle 104 is shiftable up and down relative to the vehicle body 106 with maintenance of parallelism. A phantom straight line 120 which connects pivoting centers of the pivot joints 114 and 118 provides the well known king pin axis.
Such a double wishbone type suspension requires a relatively large mounting space, particularly when the upper and lower arms 108 and 110 are made long enough to provide a good linearity in the up and down or bounding and rebounding movement of the vehicle wheel relative to the vehicle body. Particularly, the space required for the upper arm 108 often interferes with the space required for an engine or a transmission. Therefore, it is desired from the view point of mounting space that the arms, particularly the upper arm is made much shorter than desirable from the view point of ensuring the linearity in the movement of the vehicle wheel.
On the other hand, in a substantially parallelogrammic double wishbone link mechanism such as shown in FIG. 1, a camber angle of the vehicle wheel which the vehicle wheel expands relative to the vehicle body and which is referred to as "relative camber angle" hereinbelow, in contrast to the so called camber angle defined as an angle which the vehicle wheel expands relative to a straight line perpendicular to a road surface, does not change according to the up and down movement of the vehicle wheel relative to the vehicle body, i.e. the bounding and rebounding of the vehicle wheel. Such a performance of the relative camber angle is shown in a diagram in FIG. 4, in which the ordinate represents the up and down movement of the vehicle wheel relative to the vehicle body, i.e. the bounding and rebounding, while the abscissa represents the above-mentioned relative camber angle. The vertical solid line A coinciding with the ordinate axis represents the performance in respect of the relative camber angle of the suspension link mechanism shown in FIG. 1.
For an improvement of a turn running performance of the vehicle it is considered to be desirable that the relative camber angle decreases (becomes negative, i.e. top of vehicle wheel moves inboard) along with the bounding of the vehicle wheel, while it increases (become positive, i.e. top of vehicle wheel moves outboard) along with the rebounding of the vehicle wheel, so that the cambering of the vehicle wheel to the outside of a turning due to the rolling of the vehicle body to the outside of the turning is thereby cancelled.
In order to obtain such a cambering performance it is considered to incline the upper arm 108 in the double wishbone type suspension as shown in FIG. 2, so that its outer end connected with the knuckle by the pivot joint 114 is higher than its inner end connected with the vehicle body by the pivot joint 112, as compared with the lower arm 110. By so inclining the upper arm 108 relative to the lower arm 110, the above-mentioned relative camber angle changes to be more negative along with more bounding of the vehicle wheel and to be more positive along with more rebounding of the vehicle wheel, as shown by a dot-dash line B in FIG. 4. It is considered to be desirable for such a purpose of improving the turn running performance of the vehicle that the relative camber angle changes generally inversely symmetrically at a certain moderate rate according to the bounding and rebounding of the vehicle wheel so that the performance line of the relative camber angle versus bounding and rebounding wheel stroke expressed in a graph such as shown in FIG. 4 is a relatively straight line having a moderate inclination angle relative to the ordinate axis, like the above-mentioned line B. Such a performance line will become more straight as the upper and lower arms in the double wishbone type suspension are made longer.
However, the arm length, particularly that of the upper arm in the double wishbone type suspension is often restricted by an engine or a transmission, as diagrammatically shown in FIG. 3 by a shadowed obstacle. When the upper arm 108 is made shorter as shown in FIG. 3, the performance line of the relative camber angle versus bounding and rebounding wheel stroke is deformed as shown by a two dot-dash line C in FIG. 4, so that the relative camber angle increases at a too high rate in the negative direction along with increase of the bounding of the vehicle wheel, whereas the relative camber angle does not increase sufficiently in the positive direction along with increase of the rebounding of the vehicle wheel, saturating too early and turning into a decreasing performance along with further increase of the rebounding of the vehicle wheel, as is apparent from FIG. 4.